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Add disclaimer on size assertion macro #115087

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Aug 22, 2023
Merged

Add disclaimer on size assertion macro #115087

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1b9159e
Add disclaimer on size assertion macro
Noratrieb Aug 22, 2023
d16e9c3
Convert it into a warning
Noratrieb Aug 22, 2023
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12 changes: 12 additions & 0 deletions compiler/rustc_index/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -29,6 +29,18 @@ pub use {idx::Idx, slice::IndexSlice, vec::IndexVec};
pub use rustc_macros::newtype_index;

/// Type size assertion. The first argument is a type and the second argument is its expected size.
///
/// <div class="warning">
///
/// Emitting hard errors from size assertions like this is generally not
/// recommended, especially in libraries, because they can cause build failures if the layout
/// algorithm or dependencies change. Here in rustc we control the toolchain and layout algorithm,
/// so the former is not a problem. For the latter we have a lockfile as rustc is an application and
/// precompiled library.
///
/// Short version: Don't copy this macro into your own code. Use a `#[test]` instead.
///
/// </div>
#[macro_export]
macro_rules! static_assert_size {
($ty:ty, $size:expr) => {
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